Scaling behaviour of magnetization for temperatures in the vicinity of, and far from, the ferromagnetic - paramagnetic phase transition in amorphous Fe_90-xCo_xZr₁₀ and Fe_90+yZr_10-y alloys

Abstract

Asymptotic critical exponents and amplitudes as well as the leading 'correction-to-scaling' (CTS ) amplitudes have been accurately determined through an elaborate analysis of magnetization data taken on amorphous Fe_90-xCo_xZr₁₀ (0 ≤ x ≤ 6)and Fe_90+yZr₁₀-y (y=0,1) alloys in the critical region. Consistent with the Harris criterion, asymptotic critical exponents and the universal amplitude ratio Dm₀^δ/h₀ do not depend on composition and possess values the same as those predicted by theory for an ordered spin system with n = d = 3. The leading amplitude ratio a_ml^-/a_xl⁺, which is characteristic of ferromagnets with quenched random disorder and for which no theoretical estimate is presently available, is composition independent and probably universal. The fraction of spins actually participating in the ferromagnetic (FM) - paramagnetic (PM) transition occurring at T=T_cis small and increases with Co substitution. While the magnetic equation of state (MES) in linear scaling variables and its counterpart in nonlinear scaling variables, valid for a second-order phase transition, form equivalent descriptions of magnetization, M(T,H), data in the asymptotic critical region (ACR), the latter version of MES alone reproduces closely the observed M(T,H) behaviour in a temperature range as wide as 0.45T_c≤ T ≤ 1.5T_c. Nonanalytic CTS terms dominate over analytic ones in the ACR but the reverse is true for temperatures outside the ACR. Initial susceptibility follows the generalized Curie - Weiss law from T_c≈ 1.5T_cto and thereby permits an accurate determination of atomic moment in the PM state. The results of the present investigation provide strong experimental evidence for weak itinerant ferromagnetism in the glassy alloys in question.